Method of recovering tin from in bearing materials



United States atet METHOD OF RECDVERING TIN FROM TIN BEARING MATERIALSLyall J. Lichty, Ottawa, Ontario, Canada, assignor to QuebecMetallurgical Industries Limited, Toronto, Gntario, Canada, a company ofCanada No Drawing. Application September 13, 1952, Serial No. 309,548

3 Claims. (Cl. 7585) The present invention relates to the recovery oftin from tin bearing materials, such as ore, slag and concentrates.

The literature on the metallurgy of tin indicates that the smelting oftin ore has presented great difficulties. Thus, C. L. Mantell in hisbook entitled Tin, second edition, Reinhold Publishing Corporation, NewYork, 1949, indicates the following ditficulties. It states that tinoxide readily combines with silica to form tin silicates. Consequently,a considerable amount of tin invariably goes into the slag in the formof readily fusible tin silicates mixed with other complex silicateswhich make up the slag. On the other hand, if an extremely basic slag isused, tin oxide will act as an acid and enter the slag. Slag produced inthe first-run smelting of tin concentrates invariably contains so muchtin that it must be retreated before being discarded. Smelters canhandle foul Bolivian ores only with great ditficulty. Millions of tonsof low-grade ore thus far have no commercial value.

The prior art also indicates that silicon is not an eflective reducingagent for the reduction of tin from its ores and slag. Thus, the UnitedStates patents to Lamy No. 1,518,742 and to Lamy and Gagnaux No.1,826,552 describe processes for recovering tin from its ores or fromslag containing tin by reduction with a suitable reducing agent which isnot identified. In addition to the reducing agent, silicon orferrosilicon is added for the purpose of combining with and acting as acollector of iron. The tin and the ferrosilicon separate on coolingowing to their diiferent densities. The process of the latter patentdiifers from the former in that the composition of the added siliconcontaining material is such that the iron alloy formed therewithcontains a minimum of 30 per cent silicon.

The present invention is based upon the discovery that silicon is aneffective reducing agent for the recovery of tin from tin containingmaterials, such as ores, concentrates, slag, etc., under certainconditions. The invention is applicable for the recovery of tin frommaterials containing not more than about 20 per cent of tin and whichare essentially oxygen compounds of tin, iron, silicon, aluminum,calcium and magnesium and in which the ratio of the combined amounts byweight of lime, alumina, magnesia and iron oxide to silica issubstantially greater than one and the ratio of iron to tin is not lessthan about 1.5 to 1. When such a material is melted in a suitablefurnace at a temperature between about 1,300 to 1,500 C. with an amountof silicon at least as great as the amount theoretically required toreduce all the iron oxide, computed as ferrous oxide, to metal, an alloycontaining substantially equal amounts of tin and iron is obtainedtogether with a slag containing not substantially more than 0.1 per centtin. The amount of silicon used, preferably, should not be substantiallymore than that theo retically required to reduce to metal the combinedamounts of iron oxide and tin oxide computed as ferrous oxide andstannic oxide. Most satisfactory results have been obtained when thecomposition of the furnace charge ice is such that the ratio of thecombined weights of the basic components, such as lime, alumina andmagnesia, to the weight of acidic components, such as silica, in theslag produced is substantially greater than one. To assure these resultsthe composition of the charge may be adjusted by adding a basicmaterial, such as lime, when necessary.

The iron-tin alloy thus produced then may bemelted with ferrosilicon andpoured into a suitable mold. When the ferrosilicon contains about percent silicon, the amount used may be between 50 to per cent of theweight of the alloy treated. Nearly all the tin is found at the bottomof the cold casting as 97-98 per cent tin, while the upper portionconsists of brittle ferrosilicon which can be crushed and used forfurther precipitation.

While the present invention contemplates the' use of silicon as thereducing agent in its first stage, that is, in the recovery of thetin-iron alloy from ore concentrates, slag, etc., it is more practicalto employ an alloy of silicon as the reducing agent, such asferrosilicon. Similar results can be obtained when other known reducingagents for iron oxide are used in conjunction with silicon orferrosilicon, such as aluminum, calcium, magnesium, etc. For example,other alloys such as calcium carbide or calcium silicide may be mixedwith ferrosilicon. The

effective reducing agent, however, should be predominate-' Texas Citywas treated and had approximately the following composition:

Percent SiOz 41.5 FeO 15.6 Al203 18.5 0210 20.5 MgO 0.58 Sulfur 0.16 Tin0.95

100 pounds of this finely divided slag was mixed with 5 pounds of afinely divided alloy containing 66.5 per cent silicon, 8 per centaluminum and 25 per cent iron and the mixture was melted in an electricfurnace at a temperature between 1,300 and 1,500" C. The heating wascontinued for 1 /2 hours to assure completion of the reaction and thereaction mass was poured into a mold to cool. A button of metal weighing2.1 pounds was recovered from the bottom of the casting which wascomposed of iron and tin except for incidental impurities. The slagproduced contained 0.12 percent tin. The recovery of tin in the iron-tinalloy metal button was 89.1 percent.

Example 2 In this example a low grade Bolivian tin concentrate wastreated and had approximately the following composition:

100 pounds'of this concentrate, crushed to minus 100 mesh, wasmixed with9'pounds of the same finely divided alloy used in Example 1 and themixture was melted in an electric furnace at a temperature of 1,300 to1,500 C. The heating was Continued for l /zhours to assure completion ofthe reaction and the reaction mass was poured into a mold to cool. Abutton of metal weighing 25.2 pounds was recovered from the bottom ofthe casting which was composed of iron and tin exceptfor incidentalimpurities. Theslag produced contained 0.1 percent tin. The recovery oftin in the iron-tin alloy metal button was 99.3 percent.

While I'do not wish to limit the invention and the appended claims toany'theory, I believe that the reaction may take place as follows. Themolten mass of ore or concentrates contains a'piuralityof atoms, such asatoms of oxygen, tin, iron, aluminum, etc. Some of these atoms havepositively charged electrons while others have negatively chargedelectrons and form an electrically neutral mass or pattern. When siliconis introduced into the molten mass, its positively charged electronsupset the neutrality of the electrically neutral pattern and replacesome of the positively charged electrons previously preseiit, such'astho'se'carried by the tin atoms, and as a result atoms of tin areprecipitated.

I claim: I

l. The method for obtaining a high recovery of tin from materialscontaining not more than about 20 per cent of tin and which areessentially oxygen compounds of tin, iron, silicon, aluminum, calciumand magnesium and in which the ratio of the combined amount by weight oflime, alumina, magnesia and iron oxide to silica is greater than one andnot greater than about 5 and the ratio'of iron to tin is not less thanabout 1.5 and not greater than about 12 which comprises melting a finelydivided mixture comprising essentially said material and a reducingagent which comprises essentially silicon, recovering from the reactionmass the major portion of the tin in said material as an alloycontaining substantially equal amounts by weight of tin and iron, andcontrolling the composition of said mixture to produce a slag in whichthe ratio of the weights of basic components to acidic components isgreater than one, the amount of reducing agent used being at least equalto the amount theoretically required to reduceto metal all the ironoxide in said material and being not more than about the amounttheoretically required to reduce to metal the combined amounts of ironoxide and tin oxide in said material when the iron oxide and tin oxideare computed as ferrous oxide and stannic oxide.

.2. The method as described by claim 1 in which the reducing agentincludes ferros'ilicon.

3. The method as described by claim 1 in which the reducing agentincludes an alloy of aluminum, silicon, and iron.

References Cited in the file of this patent UNITED sTATEs PATENTS LamyDec. 9, 1924 Lamyet'al. Oct. 6, 1931

1. THE METHOD FOR OBTAINING A HIGH RECOVERY OF TIN FROM MATERIALSCONTAINING NOT MORE THAN ABOUT 20 PER CENT OF TIN AND WHICH AREESSENTIALLY OXYGEN COMPOUNDS OF TIN, IRON, SILICON, ALUMINUM, CALCIUMAND MAGNESIUM AND IN WHICH THE RATIO OF THE COMBINED AMOUNT BY WEIGHT OFLIME, ALUMINA, MAGNESIA AND IRON OXIDE TO SILICA IS GREATER THAN ONE ANDNOT GREATER THAN ABOUT 5 AND THE RATIO OF IRON TO TIN IS NOT LESS THANABOUT 1.5 AND NOT GREATER THAN ABOUT 12 WHICH COMPRISES MELTING A FINELYDIVIDED MIXTURE COMPRISING ESSENTIALLY SAID MATERIAL AND A REDUCINGAGENT WHICH COMPRISES ESSENTIALLY SILICON, RECOVERING FROM THE REACTIONMASS THE MAJOR PORTION OF THE TIN IN SAID MATERIAL AS AN ALLOYCONTAINING SUBSTANTIALLY EQUAL AMOUNTS BY WEIGHT OF TIN AND IRON, ANDCONTROLLING THE COMPOSITION OF SAID MIXTURE TO PRODUCE A SLAG IN WHICHTHE RATIO OF THE WEIGHTS OF BASIC COMPONENTS TO ACIDIC COMPONENTS ISGREATER THAN ONE, THE AMOUNT OF REDUCING AGENT USED BEING AT LEAST EQUALTO THE AMOUNT THEORETICALLY REQUIRED TO REDUCE TO METAL ALL THE IRONOXIDE IN SAID MATERIAL AND BEING NOT MORE THAN ABOUT THE AMOUNTTHEORETICALLY REQUIRED TO REDUCE TO METAL THE COMBINED AMOUNTS OF IRONOXIDE AND TIN OXIDE IN SAID MATERIAL WHEN THE IRON OXIDE TIN OXIDE ARECOMPUTED AS FERROUS OXIDE AND STANNIC OXIDE.